| 3-Chloro- and 3-bromo-3H-diazirines can be prepared by the reductive dehalogenation of the corresponding N,N,N'-trichloroamidines with chloride or bromide ions. This method enables the preparation of the novel 3-carboalkoxy-3-halodiazirines ( 1-54) in good yields and 3-halo-3-phenyldiazirines (1-28 and 1-48) in high yields. The attempted preparations of other novel diazirines, 3-halo- (1-100), 3,3-dihalo- (1-106) and 3-cyano-3-halo- (1-112), have not been successful; alternative reaction pathways are proposed for these compounds.; A combined experimental and computational study on the 1H-to-3 H-halo-diazirine conversion has been performed. 1H-Chlorodiazirines isomerize to 3H-chlorodiazirines by an SN2' reaction or via polar transition structures (in some cases resembling diazirinium-chloride ion pairs). The former pathway is preferred by diazirines substituted with electron-withdrawing groups, while the latter pathway is predominant with diazirines bearing electron-donating substituents.; Bromo(carbomethoxy)carbene (3-82c) is predicted at the B3LYP/6-311+ G(3df,2p)//6-31G(d) level to be a ground-state singlet, located 4.0-4.5 kcal/mol below the triplet (including corrections). The isolation of carbomethoxy(chloro)-carbene (3-82b) and bromo(carbobutoxy)carbene (3-82i) in cryogenic argon matrices by photolysis of the corresponding diazirines has been attempted. However, only the products of the follow-up reactions of vibrationally excited 3-82, alkoxy(halo)ketenes 3-97b,e and 2-halo-beta-lactones 3-103a,d, have been observed by IR spectroscopy.; An improved method for the preparation of bishomohexaprismadienone ( 4-21), a key intermediate en route to hexaprismane (4-4), has been developed. Dibromo-dimesylate 4-72 is reductively cleaved under dissolving-metal conditions to the diacetakdiene 4-46, a direct precursor of 4-21. alpha,alpha'-Functionalization of 4-21 has been attempted. |
